Hi John,..A pearl is formed when a grain of sand gets inside of a oyster's shell,..This "irritates" the oyster, which causes the oyster to "secrete" a fluid into the granual of sand. This fluid coats the sand & hardens into a pearl,..This is an "ongoing" process, so that the pearl starts out small, but continues to grow, throughout the life of the oyster,. Tecopa Jack.
